Zinc alloy



Patented Apr.'20,1943

ZINC ALLOY John R. Daesen, Oak Park, 111.

N Drawing.

Application September 18, 1940,

Serial No. 357,313

(Cl. lift-11.5)

15 Claims.

This invention relates to a new type of zinc alloy for use either in the cast or wrought form.

The invention has for its object the production of a type of a zinc alloy which has superior physical and chemical properties and stability. Specifically, the invention provides such an alloy which has a fine grain size, and increased hardness, strength and toughness, and increased resistance to softening on heating to elevated temperatures.

Still a further object of the invention resides in treating such alloys to enhance the hardness and creep resistance.

Other objects of the invention will be apparent from the following description and claims.

As is well known, zinc is available commercially in several main types, as follows:

(1) Very pure zinc, i. e. zinc which is 99.90% pure or purer. This metal is very soft and ductile, recrystallizes at room temperature and is very stable.

(2) Common zinc of Brass Special or Prime Western grade. This material is a natural alloy of zinc with varying proportions of iron, lead and cadmium. These impurities make the metal harder, less ductile, but still chemically stable.

(3) Zinc alloys, used usually in die casting, which contain aluminum in substantial amounts (1% or more). These alloys are hard, less ductile than pure zinc and are chemically unstable. Their stability is improved by small additions of other metals and by a painfully rigorous exclusion of all but the most minute traces of lead, tin and cadmium.

(4) Zinc alloyed with about 1% of copper with or without small additions of other metals. These alloys are fairly hard, fairly ductile and are chemically permanent. They are used chiefly in rolled form and are not particularly effective in resisting softening or heating.

My invention, as will be shown, results in an alloy which is superior to any of these four types of available zinc.

Before arriving at the invention, I carried out a great many experiments in an attempt to form zinc alloys of fine grain size and increased strength and toughness and resistance to softening on heating to elevated temperatures. My experiments have involved the addition to zinc of metals of high melting point (i. e. over 3000 F.). It was hoped that the addition of these metals would impart to the alloy the properties recited above. However, most of the metals with which I experimented could not be alloyed with zinc by the usual commercial means and some of them segregated badly after they were alloyed with zinc so as to be of no use commercially. I have discovered that both of these drawbacks relate to the same fundamental property of zinc and that they can be obviated if the alloy is compounded in the manner described herein.

The invention is based on the following reasonn Two metals which react to each other to form alloys yield a product which may be characterized by any of three degrees of association. (1) If the affinity of the metals is very great, as in the case of zinc with most metals, the product is an intermetallic compound embedded in an excess of one of the reacting metals. (2) If the aflmity is somewhat less, as in the case with copper, silver and gold, the product is a solid solution which appears as homogeneous phase. (3) If the affinity is still less, the melt on cooling has a. eutectic structure or one in which discrete particles of both metals settle out in a finely dispersed condition. Zinc forms such alloys with tin, bismuth and, in certain ranges of composition, with cadmium and mercury, for example.

In view of the low melting point of zinc the intermetallic compounds formed by zinc with the high melting metals are all of much higher melting point than zinc. When these metals are added to a bath of molten zinc for alloying, a solid layer of intermetallic compound forms on them and is an effective seal to prevent further alloying action. In this way only a negligible amount of the addition metal reacts with the zinc and under usual conditions this is drawn out of the melt with the unalloyed metal.

An underlying concept of the invention is that if the reacting metals have less affinity for each other, they might form the second above-mentioned class of reaction product, that is, a solid solution or, indeed, a liquid solution at the alloying temperature which would diffuse readily throughout the melt and so expose fresh surfaces of the high melting metal to the zinc for continued alloying action. In accordance with the invention, therefore, the aflinity of the molten zinc is reduced by first alloying with it an appreciable amount of copper. I have found that in this way it is possible to incorporate substantial amounts of high melting metals with zinc.

All of the alloys in accordance with my invention are thus made up of zinc and copper with one or more additional metals which have high melting points, that is, melting points above I The effective copper range of the alloys my invention is 2.00% to 3.00% with the preferred percentage for most purposes about 2.20%. In some cases, however, copper may be employed in amounts up to In compounding the alloys it is sometimes advisable to make a master alloy of zinc, copper and a high melting metal in which the two latter elements are present in considerably higher percentages than in the first alloy. The high melting metals which I have found satisfactory and all of which melt at over 3000 F. are zirconium, titanium, vanadium, chromium, columbium, molybdenum, tantalum, tungsten and uranium.

Beryllium is a border line case which confers the advantages of the invention to a limited extent but it is particularly valuable for the special property of prevention of oxidation of the 2.20% copper alloy when heated twenty-four hours at 700 F. in the presence 01 air.

These high melting point metals are used either singly or in combination in amounts ranging from 0.02% to 0.50% in zinc containing, for example, from 2% to 3% copper.

Elements tested and found inoperative in the beneficial sense described include iron, cobalt,

nickel, manganese and antimony.

The high melting metals proposed begin to show their effect at concentrations of 0.02% or thereabout and a gradual improvement in physical properties results with increasing content to about 0.50%. When only one of the high melting metals is used a content of 0.20% is usually satisfactory. It is significant to note that while these high melting metals have a slight hardening effect in zinc or in zinc alloys containing 1% or less of copper, many attempts have shown it to be impossible to disseminate evenly more than about 0.05% of these metals in such alloys, and when greater amounts were added no improvement in physical properties was found with increasing percentage of the high melting metal over 0.05%. These alloys containing 1% or less of copper do not have the superior resistance to cold flow characterized by zinc alloys with 2% or more of copper together with the high melting metals.

It is true that alloys of 1% copper with minute additions of magnesium or lithium have high creep resistance, but these alloys do not maintain their physical properties on re-melting and the proportions of the alkali metals must be very carefully controlled to avoid excessive brittleness. There is some indication that the hardness oi! these alloys with alkali metals is due to the formation of an oxidized product in the alloy, which is a much harder variable to control than a simple metallic addition. Some specific examples of the invention are as follows:

Copper 2.20 Vanadium .05 Zinc Balance Copper 2.20 Tungsten .05 Zinc Balance Copper 2.20 Zirconium .22 Titanium .22 Zinc Balance Copper 2.20 Chromium .22 Vanadium .22 Zinc Balance Copper 2.20 Columbium .20 Molyb n .10 Zinc Balance Copper 2.20 Beryllium .05 Zinc Balance Copper 2.20 Tantalum .10 Tungsten .22 Zinc Balance Copper 2.20 Chromium .20 Titanium .10 Zinc Q. Balance Copper 2.20 Chromium .05 Molybdenum-.. .12 Iron .03 Zinc Balance No.13:

Copper 2.00 Titanium .04 Molybdenum .12 Iron- .07 Zinc Balance Copper 2.20 Zirconium .05 Titanium .05 Chromium .05 Vanadium .05 Tungsten .05 Zinc Balance .or swelling, even if compounded on an impure zinc base. All oi the five grades of zinc set up by the American Society for Testing Materials (see Zinc and Its-Alloys," Bureau of Standards Circular No. 395, page 27) may be used in my alloys, but for maximum ductility and toughness the natural impurities lead, iron and cadmium should be at a minimum.

when zinc alloys containing copper and a third element, as above described, are cast in iron of this treatment to exert the maximum hardening effect without the need of a subsequent precipitating anneal. This would not be strange in molds, the alloy has a duplex structure consistview of the low melting point of zinc. ing of a ground mass of zinc containing some of The table below shows the effect of various heat the alloying material in solution and a dispersed treatments on hardness of a series of alloys of phase of particles richer in copper than the zinc containing 2.20% copper and a third element ground mass and containing zinc and some of as shown in column 1. Columns 7, 8 and 9 show the other alloy materials. In this condition, dethe results of heat treatments performed on alpending on which of the high melting metals are loys previously heat treated as in column 6. All used, the alloys have favorable physical propertests refer to alloys rolled to .010 to .030" gauge ties, such as hardness, ductility and creep resistwith the exception of column 2. The values ance. given are Rockwell H numbers (60 kg. load,

With the exception of beryllium, which I have dia. steel ball) Col. 1 Col. 2 Col. 3 Col. 4 Col. 5 Col. 6 Col. 7 Col. 8 Col. 9

Annsal Anneal Anneal 24 hrs. Anneal Anneal Anneal Cast Rolled 24 hrs. 2 hrs. 700 F. 2 hrs. 2 hrs. 2 hrs.

280 F. 400 F. and 200 F. 400 F. 000 F.

quench 07 101 as 00 07. 5 91. 5 05 00. 5 90. a 07 91 07 101 104 I 102 101 02 05 e0. 5 05 101 101 103 101. 5 s0. 5 s1 80 0s. 5 00 100 101. 5 101 as 01. 5 01. s 02 0s 07 0s. 5 as 89.5 05 02. s 04 101 101.5 100 101. 5

stated to be a borderline case, it will be noted The following table showing changes in Rockthat all of the addition metals I have tried and well H hardness resulting from the heat treathave found satisfactory, appear in even numbered ment of cast alloys of zinc with copper and other series of groups IV, V and VI of the periodic table. alloying elements as well as zinc with copper It would appear, therefore, that hafnium and alone shows first that copper alone is not satisthorium, which also fall in this category, would factory for maintenance of high hardness on anlikewise be satisfactory. nealing. It also shows that beryllium, although In accordance with another phase of the innot as efiective in increasing hardness on anneal vention, the hardness and increased resistance as the elements with melting points over 3000 are enhanced, in most cases, by subjecting the F. does prevent loss of hardness from the origialloys to elevated temperatures. For example, alnal cast or rolled state. Finally, it shows that loys using as a third element zirconium, titanium, the presenceof iron in the alloys may result in chromium or vanadium increase in hardness by a drop in hardness at extreme annealing tembeing rolled at temperatures of 300 to 400 F., and perature (600 F.) in alloys which without iron this hardness remains when this degree of heat maintain their hardness at a 600 F. anneal. The is used in a subsequent anneal for two hours. anneals of columns 4, 5 and 6 were done on al- Alloys using columbium or molybdenum as a loys previously annealed as in column 3. third element do not develop full hardness on 5 rolling but require ananneal at 400 F. Alloys COM C0 Co Co] 4 5 6 containing as a third element tantalum or tung- Amml sten require heating to 700 to 750 F. and quenching to bring out their run hardness. It will be 1 1? st v o i'. $3523 33?? 2132 noted that the reaction to heat varies with the balance ggg F melting point of the alloying metal, the higher the melting point the higher the temperature 220% Cu V 9L5 91 93 815 85 5 needed to bring out maximum hardness. This ;-%S% g 88.5 94 96.5 155' latter treatment evidently puts all of the alloy- 92,5 925 9L5 94 5 93 lng material into solid solution in the zinc or at Cu 89 5 9 least in the form of an extremely fine precipitate. 2.00%61i' ;"'.0i%' 9 100 m5 Subsequent anneals with slow cooling at tem- Eggm 94 9 peratures up to 600 F. cause the precipitation 4.00%O 1 ".0;%' 4 in more massive form ofsome of the copper and 1 i f 100 97 the third alloying element, but the hardness is 65 200 00 F300; 1m 101 not substantially reduced except when the 3 3 96 99 99 l 102 1 0. amount of the third element is low. For example, 'or+ 05% 'li 5 an alloy of 2.20% copper and .22% titanium 03% N 91 95 l 7- maintained its hardness up to 600 F. but an alloy of 2.20% copper and .05% titanium main- It will be obvious that for some purposes the tained its hardness to 400 F. only and lost much alloys may contain iron without impairing their of it at 600 F. usefulness, and this will be an economic advantage The fact that subsequent precipitating anneals with certain of the high melting metals, which do not raise the hardness above that obtained are cheap in the form of form alloys but more with the 700 F. anneal and quench is believed to 7 expensive in the pure state or alloyed with copper.

The same holds true for moderate incidental contents of nickel or manganese.

The alloys containing copper and beryllium did not lose their original bright metallic sheen in the 24 hour anneal at 700 F. and it is therefore evident that beryllium is indicated as an addition with or without another high melting metal when a bright finish is desired on the alloys after heat treatment.

The following table, shows the changes in Rockwell H hardness on annealing of a series of alloys all containing .05% each of zirconium, titanium, chromium, vanadium and tungsten, with variable copper content, and in one case with an addition of lead and cadmium, the natural impurities of zinc. As before, the treatments oi. columns 7, 8, and 9 were done on alloys previously treated as in column 6. All alloys are in the rolled form except those in column 2. a

treatment at 700 F. and subsequent quench coalesce and grow in size on subsequent heating to high temperatures with slow cooling. Some of these particles locate themselves along grain boundaries and cause reduced ductility of the alloys. The heat treating schedules shown are not oflered as the optimum treatment for any of the alloys for any special use, but merely show the eiIect of elevated temperatures in increasing the hardness and creep resistance of the alloys.

In general the maximum hardness is developed by heating the 2.20% copper alloys at 700 F. for a number of hours depending on the mass of the article and quenching. Higher copper contents require higher soaking temperatures. The 2.70% copper alloys must be heated just under the melting point to insure solution of all or the alloying material. For some purposes Col. 1 Col. 2 Col. 3 Col. 4 Col. 5 Col. 6 Col. 7 Col. 8 C]. 9

Anneal Anneal Anneal 24 hrs. Anneal Annoal Anneal Content Cast Rolled 24 hrs. 2 hrs 700 F. 2 hrs. 2 hrs. 2 hrs.

280 1. 400 F and 200 F. 400 F. 600 F.

quench 1.1 0 Cu 91.5 100 97 101 ill 87. K8. 5 9O 2, 0 Cu 95. 5 102 99. 5 102 101 98.5 l00 I01. 5 2.70% C 97 100 96 101. 0 101 101. 5 102 102 2.20% Cu, Pb,

It will be noted that the 1.10% copper alloy loses its hardness on continued exposure to elevated temperatures and the 2.70% copper alloy is no better in this regard than the 2.20% copper alloy. The presence of .10% each of lead and cadmium in the 2.20% copper alloy is shown to result in increased hardness as rolled and at low temperature anneals but reduced hardness at more elevated temperatures. This series establishes the effective copper range as about 2.00 to 3.00% copper.

Further evidence regarding the upper limit for copper for optimum effect is given by the following table which compares the Rockwell H hardness of alloys containing vanadium and chromium with copper contents of 2.20% and 4.00%. As above the treatments of columns 7, 8 and 9 are done on alloys previously treated as in column 6.

the alloys will reach a satisfactory condition in the cast or rolled state without further heat treatment.

An important feature of the invention lies in the fact that I have discovered that the higher the melting point of the third alloying element the slower it is precipitated and the finer its particles for a given heat treatment. It is recognlzed that dispersed elements of large molecular or atomic size difiuse and precipitate more slowly than do those of smaller size. Molecular size of the dispersed material rather than melting point may be the regulating factor here. It is apparent therefore that the alloys of the invention form a continuous series of which each member has its particular value under certain conditions of use. The lower melting point metals are indicated when it is desired to develop the All alloys are rolled except those of column 2. maximum hardness of the alloys merely by the C01, 1 Col. 2 Col. 3 Col. 4 Col. 5 Col. 6 (01. 7 Col. 8 Col. 9

A eal A al 24 h A um um rs nneal 1 Ann I A 1 Analysis balance zinc Cast Rolled 24 hrs. 2 hrs. 700 F 2 hrs. 2 hr 2 li r fs 280 F. 400 F. and 200 F. 400 F. 000 F.

quench 2.20 Cu .227 v 90.5 97 91 97 101 104 102 1 .003; Cu: 0% v 99.6 98 97.5 101 89. 5 90 05 30.5 Q o 32% c1- 97 101 9B 99 07.5 97.5 95 00.5 430% 4 o 102.5 98 95.0 90. 5 102 99. 5 07 9o. 5

It appears that while the same ratio of copper content to content of high melting metal is maintained, the increase in alloying elements has reduced, rather than increased, hardness at elevated temperatures.

Alloys containing 2.20% copper and 'a third metal as disclosed can be rolled to thin gauges without cracking at the edges, while with higher I copper there is more tendency for edge cracking.

While the hardness of the alloys of the invention persists even after heating to elevated temperatures, there is a change in the alloys as shown by the micro-structures. The finely precipitated particles resulting from the solution developed in rolling. The formed articles can then be heat treated to develop their full hardness and creep resistance. When the alloys are subjected to high temperatures in use and must retain not only hardness but ductility and impact vention results from the fact that severe forming operations such as wire drawing, which develop considerable heat and so soften the heretofore available workable zinc alloys, do not soften the alloys of the invention, and much greater reduction per pass, for example, in wire drawing, can be taken than with other zinc alloys. The high melting metals while fulfilling the same purpose in the alloys are therefore identical or interchangeable in only a qualitative sense. The essence of the invention, therefore, lies in the gradually changing properties provided by a series of alloys which makes them effective over a wide range of applications.

The creep resistance of the alloys of the invention is controlled by variation of the heat treatment just as is the hardness. That is, the alloys formulated with the lower melting metals of the group show greatly improved creep resistance at I low annealing or rolling temperatures, while the alloys compounded with higher melting' point metals are brought to their best state of creep resistance only by more elevated annealing temperatures. To indicate this effect, a few creep tests are listed in the table below for a number of alloys of the invention in various conditions of heat treatment.

Minutes for 1% elongation under load of 10,000 lbs. per sq. in. of zinc alloys containing 2.20% copper plus additions-show in column 1 Because it was not practical to assure exactly reproducible conditions of rolling temperature there is not the gradual change in creep resistance in the as rolled condition that Would be expected under uniform rolling conditions.

In the foregoing discussion of the invention. no mention has been made of the effect of a number of well known principles which materially affect the qualities of the alloys. Because of the novelty of these alloys as a class, a discussion of some of these principles as applied to the alloys is in order.

When fine grain size and ductility are impcrtant in the use of these alloys, the grain size is properly controlled by the rolling temperature. When a high temperature anneal after rolling is needed, the alloy may be kept in a fine grained condition either by rolling at such a temperature that there is no strain or cold work left in the alloy, or, if this is not feasible by rapid elevation of its temperature through its germinative range, in accordance with the principle described in The Sc ence of Meta s" by efi e 8; Arche page 111, paragraph 1, and page 114, paragraph 1, published in 1924.

When this method is impossible orundesirable, and when it is not desired to correct grain size by further rolling after the high temperature anneal, the composition of the alloy may be adjusted in several ways to yield a fine grain size as annealed. One simple method is' to use 'a quantity of copper or of the high melting metal greater than will be dissolved by the high tem-- perature anneal contemplated. The undissolved particles tend to restrain grain growth during the anneal. Another method is to incorporate in the alloy a quantity (say .1-.2%) of a metal which goes into solid solution in zinc such as nickel or. manganese, etc. 7

While it is not known how these zinc soluble metals act, it is presumed that they exhaust the solvent power of the zinc and keep it from dissolving as large an amount of copper at elevated temperature as would be dissolved in the absence of the zinc soluble metals nickel, manganese, etc. The undissolved copper rich precipitate would then actto prevent grain growth. This same speculation may account for the failure of these zinc soluble inetals to induce the desirable properties of hardness and creep resistance of the alloys of the invention. Their high solubility may prevent the super-saturation of the zinc lattice with copper which may be necessary for the beneficial results secured.

Of all of the high melting metals dissolved.

does in steel, that is, part of the chromium is held in solid solution in the ground mass and part of it is present in the precipitate. This is believed to be the reason for the finer grain size of alloys of the invention using chromium as compared with those using any other of the high melting metals under the same conditions 01 treatment.

The use of chromium in the alloy removes the need of the last mentioned artifice to maintain fine grain size. It is to be noted, however, that for some uses, as for. example when high creep resistance is required with minimum hardness, this dual action of chromium may be a disadvantage and the use of some other high melting metal might be preferable.

The use of aluminum in the alloy is not recommended because of its known effect in causing physical and chemical instability in zinc alloys. Tin and bismuth cause intergranular brittleness and should not be present. Alkali metals such as magnesium and lithium are preferably absent because very slight variations in amount of these metals cause wild fluctuations in properties and their effect is not constant on re-melting the alloys.

It will be apparent that the use of two or more of the high melting metals in the same alloy is indicated when favorable properties are required over a greater range of temperature than can be accommodated by an addition of only one high melting metal- This is also in order when it is not known in advance under what thermal conditions the alloy is to be used. By using a metal from both the high and the low ends of the melting point range, an alloy can be produced which has fine hardness and creep resistance as rolled and also when subjected to tempera-- tures well in excess of the rolling temperature.

W d e ca t g of n ect on are made of the alloys of the invention, the rapid chilling of the metal may entrap enough of the copper and third alloying element in solution in the zinc or at least as a very fine precipitate, so that the alloys as cast will have the improved properties described or may be given them by a relatively low temperature precipitating anneal, depending on the thermal conditions of casting and the choice of the high melting-alloy metal. a

The alloys of the invention are particularly suitable for rolled photo-engravers plates which require permanence of, hardness and creep re sistance after annealing at elevated temperatures, and must etch smoothly and rapidly in the acid" etching solution used (usually nitric acid). The fine precipitated panticles of the alloys of the invention are very uniformly distributed and of very fine particle size. They are more noble, chemically, than the ground mass, and cause, in etching, local action cells which lift out the noble particles by dissolving the ground mass adjacent and cause removal of more metal than is actually dissolved by acid, resulting in increased speed: of etch'and decreased acid consumption. The etched surfaces are very smooth because of the fineness and ubiquity of the precipitate.

when in the claims the phrase "the remainder being substantially all zinc" is employed, it is meant to include zinc of the grades referred to herein and which contain the natural impurities iron, lead and cadmium in limited amounts.

I claim:-

1. A zinc alloy; containing copper from 2 to 5%, and from .02 to .50% of at least one of theroup of grainrefining high melting point elements consisting of beryllium, zirconium, tita-. nium, vanadium, chromium, columbium, molybdenum, tantalum, tungsten and uranium, the remainder being substantially alljzinc.

2. A zinc alloy comprised offrom 2 to 5% of copper, molybdenum from .02'to 0%, the remainder being substantiallyall zinc.

a. A zinc allo comprised or about 2.20%

copper, molybdenum about 40%, the remainder being substantially-all zinc. v, v

4. A zinc alloy comprised of from 2 to 5% copper and from".02.to --.50%- vanadium, the remainder being substantially all zinc. 4

5. A zinc alloy comprised of about 2.20%.

' copper, vanadium about- 22%, the remainder being substantially all zinc.

6. A zinc alloy comprised of from 2 to 5% copper, and from .02 to .50% tungsten, the re-' mainder being'substantially all zinc.

7. A zinc alloycomprised of about 2.20% copper, tungsten'about 22%, the remainder being substantially all'zinc.

8. The process of forming. an article which comprises rolling and fabricating a zinc alloy comprisingfrom 2 to 5%, and from .02to .50%

of at least one of the group of grain refining high melting point elements consisting'of beryllium, zirconium, titanium, vanadium, chromium, columbium, molybdenum, tantalum, tungsten and uranium, the remainder being substantially all zinc, to form the'artlcle into the desired shape and then increasing at least one of the two properties hardness and creep resistance of the article by heat treatment including heating at temperatures upto 750 F.

p 9. The process of forming an article which comprises rolling and fabricating a zinc alloy comprising copperfrom 2 to 5% and from .02 to .50% vanadium, the remainder being substantially all zinc, to form the article into the deproperties hardness and creep resistance of the article by heat treatment includin temperatures up to 750. F.

ll. "I-?he process of forming an article which g heating at comprises rolling and fabricating a zinc alloy comprising copper from 2 to 5% and from -02 to .50% molybdenum, the remainderv being substantially all zinc, to form the article into the desired shape and then increasing at least one of the two properties hardness and creep resistance of the article by heat treatment including heating at temperaturesup to 750 F, p a I 12. An article of manufacture comprised of a shaped zinc alloy comprising. copper from 2 to 5%" and from .02'to .50% of at least one of the group of grain :refining high melting point elements consistingof beryllium, zirconium, titanium; vanadium, chromium, 'columbium,moiybdenum,'tantalum,tungsten and'uranium, the remainder being substantially all zinc, atle astone l" of the two properties hardness and'creep resistance of which articl has been increased by heat treatment including to 750 F. t

13. An article of manufacture comprised of a shaped zincalloy comprising copper from 2 to 5% and from .02 to .50% vanadium, fthe'reheating at temperatures up mainder being substantially all 'zincat 'least'one of the two'properties hardness andflcreep resist-.

ance of which article has beenincreased byheat treatment including heating attempei'atures up 'to750F. I

f l4. An article of manufacture comprised-of ashaped zinc'alloy comprising copper 'from 2 to 5% andfrom .02 to-.50% tungsten. the re mainder being substantially all zinc,atleast oneof the two properties hardness and creep resist: ance or which articlehas been increased by'heat treatment including heating at temperatures-up to 1''.

15. An article r manuf cture comprised of a Y shaped zinc alloy comprising copper from 2 to 5% and from .02 to .50% molybdenum, the re-,

mainder being substantially all zinc, at least one ofthe two properties hardness and creep resist-.

ance of which article has been increas edby' heat treatment includingheating at temperatures up to750F. q I JOHNRDAESEN. 

